Optical disks that may be written once have gained wide acceptance as a means of backing up data and custom publishing. These drives use a relatively high power laser to damage the surface of a blank disk during the writing operation. The data is read by detecting the reflectivity of the disk surface utilizing a low power laser and optical detector for detecting the fraction of the light reflected by the disk surface. The disks are read with the aid of two or more low power lasers, one for reading the data bits and the others for detecting track data that is used to position the reading laser. The various beams are generated from a single high power laser by a beam splitter or equivalent optical structure.
The power needed to write the disk is typically of the order of 10 mW. The power needed for the reading operations is only of the order of 1 mW. However, to accommodate the losses inherent in the beam splitter, the high power laser must be typically 30 mW. Lasers in this power range are difficult to construct.
To provide a high power laser in the 30 mW range, edge emitting laser technology must be utilized. The single edge emitting laser is then aligned with the beam splitter and the detectors used for tracking and reading.
The need to employ edge emitting laser technology and the need to provide some form of alignment mechanism substantially increases the cost of read/write optical disks and limits the read/write mechanism to a single "head" which can operate only on one track at a time.
One drawback of optical disks has been their slow speed compared to conventional magnetic disk drives. In principle, this drawback could be overcome by using multiple read/write heads. However, the cost of the heads based on single edge emitting lasers together with the need to align the heads with respect to one another, has made such systems commercially unattractive.
Broadly, it is the object of the present invention to provide an improved read/write head for use in optical disks.
It is a further object of the present invention to provide a read/write head that may be constructed without reliance on edge emitting lasers.
It is a still further object of the present invention to provide a read/write head that can read and/or write multiple tracks on an optical disk at the same time.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.